Experiments are proposed to determine the mechanism of the related vitamin K epoxide and quinone reductase(s) and the mechanism of their inhibition by the coumarin anticoagulants and other compounds. These enzymes play a key role in the ability of vitamin K to promote blood coagulation factor biosynthesis, appear to be the pharmacologically important site of coumarin anticoagulant action, and are suitable target enzymes for the development of new classes of anticoagulants. Anticoagulants have found application in the management of stroke, cardiovascular disease, pulmonary embolism, vascular implant and heart valve replacement survival, and have recently shown promise as antineoplastic agents. Anticoagulants have also been effective rodentocides important in control of rodent born human diseases. Clinical use of coumarin anticoagulants, most commonly sodium warfarin (Coumadin), is complicated by a large number of drug potentiation interactions and undesirable side effects. Some side effects of current anticoagulants may relate to a lack of specificity of the inhibitors for the target enzyme, others may relate to inhibition of vitamin K function in extrahepatic tissues and may point to new potential applications for tissue directed vitamin K epoxide reductase inhibitors. The long term goal of these studies is the development of new classes of vitamin K epoxide reductase inhibitors. A first step is the complete elucidation of the reaction mechanism of the target enzyme. This work will involve purification and characterization of the enzyme, clarification of the relationship between the vitamin K epoxide and quinone reductase(s), chemical modification and enzyme kinetic studies, examination of known inhibitors as mechanistic probes, and the application of known reactions expected to yield site specific covalent inactivation of the enzyme. A second project will examine the tissue distribution of vitamin K epoxide reductase activity and its sensitivity to coumarin anticoagulants. Differences in the properties of the enzyme in different tissues that are detected will for a basis for segregation of anticoagulant activity from side effects and may permit application of vitamin K antagonists in situations where their anticoagulant activity is undesirable.